The invention is related generally to fasteners and more particularly, to blind fasteners having a sleeve and setting pin and means for retaining the setting pin in the sleeve.
Where access to work pieces exists on one side of the work only, blind fasteners are often used for fastening the work pieces together. The side of the work from which the fastener is applied is referred to as the "access side" and the other side is referred to as the "blind side." Many blind fasteners comprise two basic parts, a tubular sleeve and a setting pin which moves telescopically in the sleeve. The sleeve typically comprises a radially enlarged head integral with one end thereof which presses against the access side of the work pieces. The sleeve also comprises a shank through which the pin moves.
The pin comprises a "tail" or pulling section at one end which is relatively free to move through the sleeve and projects out the access side of the work pieces. The pin also comprises a head having an outer diameter which is greater than the inner diameter of the sleeve. Prior to use the sleeve and pin are assembled with the pulling section of the pin projecting from the head end of the sleeve and the head of the pin located at or near the shank or blind end of the sleeve.
With the two basic parts in telescoped relation, the fastener customarily is inserted into aligned apertures in the work pieces to be fastened together from the access side thereof, and is positioned with the head of the sleeve on the access side and with the head of the setting pin on the blind side. The pin is pulled from the access side while a restraining force is applied against the sleeve head to hold it in place. This draws the head of the pin into the sleeve shank which results in the shank being radially expanded or "upset" on the blind side to clamp the work pieces together. It is also desirable in setting a blind fastener to expand the sleeve within the apertures in the work pieces into pressure engagement with the walls thereof, thus improving the shear strength of the resulting connection.
Frequently, the work pieces which are to be fastened together are initially separated from each other and must be clamped together during fastening. To achieve this without having to clamp the pieces together by some independent means, it is desirable that the projecting portion of the shank of the sleeve on the blind side be expanded sufficiently to clamp the work pieces together before the shank portion within the apertures is expanded against the walls of the apertures. If this is not done, that is if the expansion of the shank portion within the apertures takes place before clamping, the parts will not be clamped together. This premature expansion of the fastener will lock the pieces in their separated position. Failure to properly clamp the work pieces will preclude the fastened combination from developing either the desired shear or tensile strength. Thus a satisfactory fastener must first operate to clamp the work pieces and then expand within their apertures to secure them in that position.
In prior fasteners, the larger outer diameter head of the pin engages the lesser inner diameter sleeve to form a bulged, bulb-shaped head on the blind side end of the sleeve. As the setting pin is pulled through the sleeve, the expanding sleeve first causes clamping of the work pieces to occur and then causes expansion of the sleeve within the apertures of the work pieces. To enable successful fastening, the size of the apertures in the work pieces are such that the fastener can be easily inserted but with a minimum of clearance.
In some fasteners, there exists a means to stop further movement of the pin after it has been pulled into the sleeve to a certain extent and to lock it in position. Without some locking means, the pin and sleeve may pull apart later, such as when exposed to high levels of vibration. Where the sleeve itself cannot provide the desired shear strength and the additional strength of the pin in the sleeve is required but is not available due to disengagement, unfastening of the work pieces could occur. In some devices, friction alone was used to hold the pin and sleeve together. This method of locking has been found to be inadequate in some applications. A contributing factor to a lack of adequate strength is that the pin and sleeve take on complementary tapered configurations at their juncture surfaces as the pin is drawn into the sleeve. The resulting taper is so directed that the diameter of the juncture surface increases toward the blind end, thus facilitating retrograde movement of the pin out of the sleeve. This retrograde movement may be accelerated by using the assembly in a high vibration environment. Further, the resilient metal of the pin is strained somewhat during the setting so that when the pulling force is rapidly released by fracturing the pin at the breakneck groove, the pin tends to spring back slightly. As a consequence, the clamping force on the work pieces is relaxed somewhat and the joint will loosen somewhat.
Various techniques for locking the pin and sleeve together have been developed. However, many include only a single lock and, depending upon the application, stronger locking of the pin to the sleeve may be required. For example, work pieces which may be used in a high stress or high vibration environment should have fasteners whose components are locked together strongly enough to resist any tendencies to separate when subjected to such vibration.
In view of the foregoing, it would be desirable to provide a pull-type blind fastener which is adapted to provide improved locking of the pin to the sleeve when assembled. It would also be desirable to provide a two piece blind fastener in which the pin and sleeve are mechanically locked together by two locking structures and further, a blind fastener in which the pin and sleeve are mechanically locked together by material from the sleeve.